Device isolation typically is achieved by utilizing local oxidation of silicon (“LOCOS”) or shallow trench isolation (“STI”) techniques. In the STI device isolation technique, isolation is typically achieved by forming a recess or trench in a layer that is destined to become two adjacent active areas, and filling the trench with an isolation material. The material in the trench, typically a nitride material, is referred to as a spacer. Nitride spacers, in addition to electrical isolation, may also be used as a fluid barrier.
STI is beneficial in providing higher packing density, improved isolation, and greater planarity, by avoiding the topographical irregularities encountered when using conventional thick film oxide isolation (LOCOS). In particular, the growth of thermal field oxide using a mask, such as nitride, creates an encroachment of the oxide into the active areas; this encroachment is referred to as the bird's beak effect.
High aspect ratio trenches, while theoretically desirable in reducing the footprint of a nitride spacer, present various technical problems. One significant problem is that when depositing nitride to fill a high aspect ratio trench, a vertical seam inherently occurs along the center of the trench, where the outer surfaces of deposited nitride layers on opposing vertical trench walls meet. The vertical seam generally includes gaps in which no nitride material is present. While the gaps may not degrade the electrical isolation function of a nitride spacer, the gaps are problematic in other respects. For example, in fluid barrier applications, the gaps are essentially a short circuit in the isolation capability of the nitride spacer. Moreover, the gaps are flaws which can reduce the material strength of the nitride spacer.
What is needed therefor is a spacer and method of forming a spacer that overcomes one or more problems in known spacers. It would be beneficial if the spacer and method of forming a spacer could include high aspect ratio trench forming processes while providing increased spacer strength. It would be further beneficial if the spacer and method of forming a spacer could include high aspect ratio trench forming processes while providing improved spacer isolation characteristics.